10/04 Liquefaction damage widespread

The Yomiuri Shimbun

Soil liquefaction on reclaimed land around Tokyo Bay because of the March 11 earthquake caused damage in at least 11 Tokyo wards and cities in Chiba and Kanagawa prefectures, according to tallies by local authorities.

About 1,100 homes and other buildings in these areas were destroyed or damaged, and many public facilities such as roads and parks have been rendered useless due to soil liquefaction, according to damage assessment reports obtained by The Yomiuri Shimbun.

The liquefaction-hit areas are about 400 kilometers from the focal zone of the Great East Japan Earthquake. Yet the the length and force of the magnitude-9.0 temblor was so strong it set off soil liquefaction on the largest scale ever recorded in this country, experts said.

In the cities of Chiba, Urayasu, Funabashi and Narashino in Chiba Prefecture, 30 homes and buildings were destroyed, while 1,046 other buildings suffered liquefaction-related damage.

Most severely stricken was Urayasu, where 85 percent of the land was affected by soil liquefaction. An estimated 33,000 households in the city had their water supply temporarily cut off following the quake.

Tokyo Disneyland, which is in Urayasu, suffered severe damage to its carpark due to liquefaction. It has been closed since the earthquake but is expected to reopen this month.

In Tokyo, large quantities of liquefied sand spewed from the ground in Koto Ward, while eight homes in Edogawa Ward have been left leaning, the assessment reports said.

An unspecified number of liquefaction-caused cracks were found in parks, roads and elsewhere in Minato, Chuo and Ota wards.

In Kanagawa Prefecture, six cases of subsidence-related damage were confirmed in Yokohama and Kawasaki, including at an apartment building in Kanazawa Ward, Yokohama.

University of Tokyo Prof. Ikuo Tohata, who specializes in geotechnical engineering, said: "The earthquake's hypocentral region was far away from the liquefaction-stricken areas, but the earthquake apparently ruptured faults including some beneath the sea off Ibaraki Prefecture. Hence the temblor's seismic energy was powerful enough to cause extensive damage to reclaimed areas along Tokyo Bay.

"Also, the quake's jolts lasted for a relatively long time and this may have contributed to the large-scale liquefaction," Tohata said.

(Apr. 10, 2011)